How to get rid of the space between the edge of the camera render area and the actual viewport?
You have a View Lock on the camera to view enabled.

Hit the N key and look for the checkbox title Lock camera to view, it might be one of the others but I suspect this is the guilty setting.



This is a known issue for newcomers to blender, but it is actively being worked on, you can read more about improvements relating to these controls on ‘Lock Camera To View’… It was torture to find it!

The fact that you have this happening in all blend files suggest that at some point this had been enabled and has been saved into your startup.blend file, meaning that you need to save your startup file after you've fixed the issue ( but now you know how, so it won't be a problem right? ).